From: Marton Balint <cus@passwd.hu>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 1/2] avformat/hlsenc: fall back to av_get_random_seed() when generating AES128 key
Date: Tue, 4 Jul 2023 21:30:29 +0200 (CEST)
Message-ID: <10991752-b1e9-41c0-623f-69ac11d994c9@passwd.hu> (raw)
In-Reply-To: <3b28f549-fc02-8ebf-de01-7dc1e0ae3c03@gmail.com>
On Tue, 4 Jul 2023, James Almer wrote:
> On 7/3/2023 6:52 PM, Marton Balint wrote:
>>
>>
>> On Mon, 3 Jul 2023, Anton Khirnov wrote:
>>
>>> Quoting Marton Balint (2023-07-03 22:54:41)
>>>> On Mon, 3 Jul 2023, Anton Khirnov wrote:
>>>> My patch use av_get_random_seed() which uses what the underlying OS
>>>> provides, BCrypt for Windows, /dev/urandom for Linux, arc4random() for
>>>> BSD/Mac.
>>>
>>> IOW it's a jungle of various paths, some of which are not guaranteed to
>>> be cryptographically secure. I see no such guarantees for arc4random()
>>
>> It depends on OS and version most likely.
>>
>>> from a brief web search, and the fallback get_generic_seed() certainly
>>> is not either.
>>> Granted it's only used on obscure architectures, but
>>> still.
>>
>> I am no expert on the subject, but even the generic code seems reasonably
>> secure. It gathers entropy, it uses a crypto hash to get the output. And
>> as you said, even that only used for obscure cases.
>>
>>>
>>> The doxy even says
>>>> This function tries to provide a good seed at a best effort bases.
>>>
>>>> You really think that these are significantly worse than
>>>> OpenSSL/GCrypt, so it should not be allowed to fallback to?
>>>
>>> I think we should be using cryptographically secure PRNG for generating
>>> encryption keys, or fail when they are not available. If you want to get
>>> rid of the openssl dependency, IMO the best solution is a new
>>> int av_random(uint8_t* buf, size_t len);
>>> that guarantees either cryptographically secure randomness or an error.
>>
>> Sorry, seems a bit overdesign for me, so I won't be pursuing this further.
>
> I just sent a patchset implementing a new av_random() function that uses the
> existing av_get_random_seed() entropy sources, and adds the ones used by
> hlsenc too.
> If that goes in, then this patchset can go in as well afterwards.
Thanks! I will rework the patch to use av_random() then.
Regards,
Marton
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next prev parent reply other threads:[~2023-07-04 19:33 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-02 19:30 Marton Balint
2023-07-02 19:30 ` [FFmpeg-devel] [PATCH 2/2] avformat/hlsenc: remove openssl/gcrypt random key generation Marton Balint
2023-07-03 2:21 ` Steven Liu
2023-07-03 2:20 ` [FFmpeg-devel] [PATCH 1/2] avformat/hlsenc: fall back to av_get_random_seed() when generating AES128 key Steven Liu
2023-07-03 19:23 ` Marton Balint
2023-07-03 19:33 ` James Almer
2023-07-03 20:15 ` Anton Khirnov
2023-07-03 20:54 ` Marton Balint
2023-07-03 21:09 ` Anton Khirnov
2023-07-03 21:52 ` Marton Balint
2023-07-04 19:02 ` James Almer
2023-07-04 19:30 ` Marton Balint [this message]
2023-07-06 17:01 ` [FFmpeg-devel] [PATCH] avformat/hlsenc: use av_random_bytes() for " Marton Balint
2023-07-14 19:39 ` Marton Balint
2023-07-03 23:50 ` [FFmpeg-devel] [PATCH 1/2] avformat/hlsenc: fall back to av_get_random_seed() when " Michael Niedermayer
2023-07-04 5:54 ` Anton Khirnov
2023-07-04 9:08 ` Kieran Kunhya
2023-07-04 14:37 ` James Almer
2023-07-04 15:31 ` Anton Khirnov
2023-07-04 23:50 ` Michael Niedermayer
2023-07-05 9:22 ` Anton Khirnov
2023-07-05 22:54 ` Michael Niedermayer
2023-07-06 7:52 ` Anton Khirnov
2023-07-06 23:34 ` Kieran Kunhya
2023-07-07 0:55 ` Michael Niedermayer
2023-07-07 8:05 ` Anton Khirnov
2023-07-07 14:42 ` Michael Niedermayer
2023-07-03 20:20 ` Marton Balint
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